1. Field of the Invention
The present invention relates generally to semiconductor structures and process for manufacture of "light emitting diodes" and more specifically to epitaxially depositing gallium phosphide, crack free on a silicon substrate.
In order to reduce the cost of materials and produce light emitting diode displays monolithically with silicon integrated circuits, there is great interest in forming layers of gallium phosphide on silicon substrates. The feasibility of forming such a structure rises because of the close match in lattic constants of silicon (5.43 A.degree.) and gallium phosphide (5.45 A.degree.). U.S. Pat. No. 3,766,447 overcomes the problems of mismatch between silicon and gallium phosphide by using a graded layer of a silicon-germanium alloy therebetween. It is desirable to form an epitaxial gallium phosphide film directly on the silicon substrates of high quality and eliminating the cracks formed therein by stress induced by thermal expansion.
A survey of the literature shows that epitaxial GaP films were grown on Si using electrolysis of NaPO.sub.3, NaF and Ga.sub.2 O.sub.3 (Cuomo, J. J., and Gambino, R. J., J. Electrochem. Soc.,115, 755-759 (1968)) and by decomposing a mixture of gallium triethyl and phosphorous triethyl at 485.degree. C. (Thomas, R. W., J. Electrochem. Soc., 116, 1449-1450 (1969)). GaP films were grown on sapphire using trimethyl gallium and phosphine (Manasevit, H. M., and Simpson, W. I., J. Electrochem. Soc. 116, 1725-1732 (1969)). Igarashi grew GaP films on silicon by an evaporation method and noticed crack lines running in cleavage directions on (111), (110), and (100) crystal plains. (Igarashi, Osamu, J. Appl. Phys., 41, 3190-3192 (1970)). By depositing onto silicon through windows etched into a SiO.sub.2 masking film, the GaP film cracking apparently disappeared. (Igarashi, Osamu, J. Electrochem. Soc., 119, 1430-1431 (1972)). Gallium phosphide films on silicon using eutectic epitaxy from Pb solvent and from Sn solvent have also been used. (Rosztoczy, F. E., and Stein, W. W., J. Electrochem. Soc., 119, 1119-1121 (1972)). Also, West German Patent No. 2,144,828, Mar. 30, 1972.) Chloride transport processes have also been used to form GaP on silicon substrates and cracks in the GaP layers were also observed. (Huber, H., and Winstel, G. H., Siemens Forsch. u Entwicki. Ber., 2, 171-174 (1973).)
The achievements and difficulties of the prior art are also discussed specifically in U.S. Pat. No. 3,963,538. This patent provides the gallium phosphide layer on silicon having an orientation of (100). The process described therein has not been successfully used to form a gallium phosphide layer on silicon having an orientation of (111).
U.S. Pat. No. 3,699,401 discusses the formation of gallium phosphide using phosphine and trimethyl gallium on a synthetic sapphire base with a silicon layer therebetween.
Thus there exists a need for forming crack free gallium phosphide layers on silicon substrates having a crystal orientation of (111).